1. Field of the Invention
The present invention relates to an automatic adjustment system for a reception device to correctly retrieve data that is transmitted from a transmission device. The present invention also relates to an automatic adjustment device and an automatic adjustment method.
2. Description of the Related Art
In recent years, more and more attention is being drawn to the remote control unit that controls two or more computers with one set of a keyboard, a mouse, and a display (the set will be hereinafter referred to as a “console”). Where a large number of computer systems are operated at the same time, connecting a console to each of the computer systems greatly complicates the operation and wiring of each of the systems. In such a case, the remote control unit connects one console to the computer systems, thereby enabling access from the console to the computer systems.
To correctly retrieve a signal transmitted from a transmission end to a reception end in the above system, it is necessary to correct the signal at the reception end. Especially, when cables for signal transmission and reception are changed, the correction value for accurately retrieving the data needs to be measured.
When the cable length is changed, the transmission distance also changes. As a result, a change is caused in the attenuation of the transmission signal. Such a change in the attenuation causes a serious problem in the case of an analog signal for which amplitude has a great significance. Also, phase differences among twisted pair signal lines contained in a cable present a problem. For example, when signals such as RGB signals that deeply correlate to one another in terms of the phase and would have trouble with a phase difference are transmitted over a long distance, a phase difference is caused between signals due to the difference in length between the twisted pair signal lines. This results in inaccurate data retrieval.
Japanese Unexamined Patent Publication No. 2003-46354 (Patent Document 1) discloses a structure shown in FIG. 26. In this structure, a constant voltage output circuit 202 that transmits a constant voltage signal through a cable 210 is provided in a transmission device 200. A voltage detecting circuit 222 that receives the constant voltage signal transmitted through the cable 210 is provided in a reception device 220. Also, a MPU 223 that obtains the data of the cable length based on the detected voltage, and adjusts the gain of the reception device 220 is provided in the reception device 220.
In the structure disclosed in Japanese Unexamined Patent Publication No. 2003-202828 (Patent Document 2), a signal line for transmitting a horizontal synchronization signal is also employed as well as the signal lines for transmitting RGB signals to be input from a PC. The phase difference between the horizontal synchronization signal and each of the RGB signals is detected, and the phase differences among the color signals are corrected based on the detected results.
In the structure disclosed in Patent Document 1, however, attenuation is determined from the length of the cable that is connected to the transmission device and the reception device every time the system power source is turned on, and gain adjustment is then performed on analog signals. Therefore, gain adjustment is invariably performed every time the power source is turned on, even though cables are not changed. As a result, a great time loss is caused.
In the structure disclosed in Patent Document 2, it is necessary to prepare a signal line for transmitting the horizontal synchronization signal. As a result, the device becomes large in size.